JPS5993779A - Heat accumulative material - Google Patents

Abstract

PURPOSE:A heat accumulative material having stable nucleus forming effect for a long period, capable of using effectively latent heat to be released during coagulation, obtained by adding a halide of potassium or ammonium as a nucleus forming agent for preventing supercooling to acetic acid, etc. CONSTITUTION:(A) Acetic acid or a composition of acetic acid and an acetic is blended with (B) 0.1wt% halide of potassium and/or ammonium (e.g., KCl, NH4Cl, KBr, NH4Br, etc.) as a nucleus forming agent for preventing supercooling, to give the desired heat accumulative material. EFFECT:Temperature difference between the coaglulation temperature of a heat accumulative material and the temperature of heat medium such as water, air, etc. to be subjected to heat exchange can be reduced, and heat design is made easily.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a heat storage material for air conditioning, and is used to promote solidification of acetic acid or a composition in which acetic acid is added to acetic acid and to prevent overcooling during solidification. Potassium or ammonium halide is added as a nucleating material.

Acetic acid is 16.7C when pure, and 14.C when it contains impurities such as for industrial use. It is known that it is used as a heat storage material because it solidifies and melts at a constant temperature of 50° C. or higher, and releases and absorbs latent heat at this time.

However, when acetic acid is sealed in a closed container, supercooling of 6 to 10 C occurs, and heat storage and heat radiation cannot be carried out at a predetermined temperature. The cause of this is not clear, but when acetic acid is poured into an open container, it evaporates from the surface, and as the heat of vaporization is removed, acetic acid crystals precipitate, which become nuclei and solidify. It is thought that this is because of this.

Even in a composition in which acetate is dissolved in acetic acid, supercooling does not occur in an open state, but in a sealed state, supercooling occurs at 6 to 10°C, as in the case of acetic acid, and heat storage and heat dissipation occur at a predetermined temperature. It was difficult to do.

[Purpose of the invention]

An object of the present invention is to provide a heat storage material that prevents overcooling of acetic acid or a composition obtained by adding an acetate to acetic acid, and that stores and releases heat at a constant temperature determined by the composition of the material.

In general, the phase change from liquid to solid can be divided into a crystal nucleus generation stage and a crystal growth stage centered on the nucleus. Nuclear generation requires a large amount of energy, and supercooling requires this energy, and it is known that supercooling occurs due to this energy barrier. For this reason, methods are being used to prevent overcooling by adding nuclear material.

In this case, the nuclear material exists in the liquid phase without bath dissolution, and the interfacial energy with the newly generated crystal on the interface is small.
It is known that the nucleus needs to have a size larger than a certain critical radius (the critical radius is 1 to 100 μm). In addition, crystal growth is caused by crystal planes with low molecular density (for cubic crystals, 100
, 110 and 111). As examples of such nucleating materials, the effects of barium hydroxide and strontium hydroxide on calcium chloride hexahydrate have been recognized. However, since barium hydroxide and strontium hydroxide form barium acetate and strontium acetate in acetic acid and dissolve in acetic acid, such basic inorganic substances cannot be used as nucleating materials. Furthermore, since acetic acid reacts with most organic compounds, many organic compounds cannot serve as nucleating materials. For this reason, we investigated the nucleation effect of acetic acid and neutral inorganic substances, and found that potassium chloride and ammonium chloride showed a significant nucleation effect.

Nu-kCl dissolves in acetic acid at high temperatures, but its solubility decreases as the temperature decreases and disappears at the freezing point of acetic acid. Therefore, NH4Cl crystals are precipitated prior to the solidification of acetic acid, and serve as the nucleus for the precipitation of acetic acid crystals at the solidification point of acetic acid. KC2 also shows similar solubility changes as NI-bCt and promotes acetic acid coagulation. It has also been found that in acetic acid in which acetate is completely dissolved, precipitation of crystals of acetic acid in which acetate is dissolved is promoted by NH<Ct or KCt at its freezing point.

It was also confirmed that such a nucleating effect is commonly observed in halides (anhydrides) of K and N I-14.

The heat storage material of the present invention includes acetic acid or a composition prepared by adding acetate to acetic acid, and potassium chloride, ammonium chloride, potassium bromide, ammonium bromide, potassium iodide, etc. as a nucleating material.
One or more substances selected from ammonium iodide, potassium fluoride, and ammonium fluoride are added.

] 1, 1 (5 examples) Select potassium chloride and ammonium chloride from these NH4 halides and explain their effects.

Figure 1 shows the cooling curve of pure acetic acid (99.5%).
) is when no nucleating material is added, curve (b) is when 0.1% total potassium chloride is added as a nucleating material, and curve (C) is when ammonium chloride 'i o. This is the case where i% is added. In curve (a), there is supercooling of 8C before the start of solidification, solidification starts at 7.5°C, and the temperature rises accordingly to 15. 5
The temperature is maintained at this temperature until the temperature reaches r and solidification is completed.

On the other hand, curve (b) shows that supercooling before the start of solidification is IC1 (
C) is 0.5C, which is extremely small compared to curve (a). In this case as well, the temperature rises as the solidification begins, and the temperature rises until the solidification is completed, as in curve (a). It is kept at 5U.

Figure 2 shows the cooling curve of a composition prepared by adding and dissolving 5% by weight of sodium acetate and 5% by weight of potassium acetate in acetic acid.Curve (a)
Curve (b) is the case where no nucleating material is added, curve (C) is the case where 0.1% by weight of potassium chloride is added as the nucleating material. In curve (a), there is a supercooling of 6C before solidification starts, solidification starts at 1.5C, the temperature rises accordingly, reaches 7.5C, and is maintained at this temperature until solidification is completed. .

On the other hand, curve (b) shows that the supercooling before the start of solidification is 0.6C.
, curve (C) indicates that the supercooling before the start of solidification is O. 3C curve (a
) is extremely small compared to In this case as well, the temperature increases with the start of solidification, and as in curve (a), the temperature rises to 7.5C until solidification is completed.
is maintained.

A common method of using heat storage materials is to melt the heat storage material, send a heat medium such as low-temperature water or air around the heat storage tank, and heat it with the heat released when the heat storage material solidifies. Heat is being used. At this time, if the heat storage material is supercooled below the temperature of the heat medium, the latent heat of solidification cannot be effectively extracted. Generally, when a heat storage material is used for heating or cooling, it is efficient to set the difference between the solidification-melting temperature of the heat storage material and the temperature of the heat medium before heat exchange to be 2 to 4C. For this reason, the presence of a slight amount of supercooling greatly affects heat utilization efficiency. The potassium and ammonium halides of the present invention have low solubility in acetic acid and do not form compounds with acetic acid. For this reason, potassium and ammonium halides are almost completely precipitated when the heat storage phase solidifies, and even after repeated use over a long period of time, the nucleating material will not dissolve or chemically change and lose its effectiveness. Examples of the present invention in which the nuclear effect is stable over a long period of time will be described below.

(1) Heat storage material ffi made by adding 0.01% by weight of potassium chloride as a nucleating material to industrial acetic acid (-melting point 15.0c)
4 (cycle f. heating to I' and then cooling to oC).
The temperature curve of the heat storage material was recorded for one hour by repeating the r20 surface. In this case, each round of supercooling was 1.0 C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions.

In addition, in the heating and cooling experiments of acetic acid without a nuclear detergent conducted at the same time, supercooling of 8 to 10 C occurred each time.

(2) Heat storage material - i40c made by adding 0.01% by weight of ammonium chloride as a nucleating material to industrial acetic acid (melting point 15.0C).The cycle of heating and cooling with OC1 was repeated 20 times to form a heat storage material. A temperature one hour curve was recorded. In this case, the supercooling each time was 0.5C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions.

(3) A heat storage material made by adding 0.01% potassium chloride as a nucleating material to a composition (freezing point 8C) made by adding 5% sodium acetate and 3% potassium acetate by weight to industrial acetic acid.
20 cycles of heating to 5R and cooling to -5C
The temperature one-hour curve of the heat storage material was recorded repeatedly. In this case, each supercooling was 0.6C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions.

(4) 5M sodium acetate in industrial acetic acid. ft%, potassium acetate 3Mt% total addition composition (freezing point 8C), ammonium chloride O, 01% added as a nucleating material, heat storage material was heated to 25 tl' and then cooled to -5C, the cycle was repeated 20 times. Ta.

In this case, each supercooling was 0.3C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions.

As explained above, according to the present invention, it is possible to prevent overcooling of acetic acid or a composition in which acetic acid is added to acetic acid by adding a nucleating material, so that the latent heat released during solidification can be efficiently utilized. .

Further, it is possible to reduce the difference in temperature between the solidification temperature of the heat storage material and the heat medium (water, air, etc.) to be heat exchanged, and the effect of facilitating thermal design can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the temperature curve (a) for one hour during cooling of pure acetic acid.
) shows the case without nucleating material, curve (b) shows the case when potassium chloride is added as the nucleating material, curve (C) shows the case when 0.1% by weight of each ammonium chloride is added as the nucleating material, and Fig. 2 shows the case when sodium acetate is added to acetic acid. 5Mfil% and 5% by weight of potassium acetate were added. Curve (a) shows no nucleating material and curve (b) shows potassium chloride and (
C) each uses 0.1 ammonium chloride as a nucleating material.
It is a figure when adding weight%.

Claims (1)

[Claims] ■. It is characterized by adding one or more materials selected from the group of potassium and ammonium halides as a nucleating material to completely prevent overcooling to acetic acid or a composition obtained by adding an acetate to acetic acid. Heat storage material. 2. Potassium and ammonium halides are potassium and ammonium chlorides (KCt, Nrl. Ct
) or potassium and ammonium bromide ( KBr
, NH4Br) according to claim 1.